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  Subjects -> ENGINEERING (Total: 2070 journals)
    - CHEMICAL ENGINEERING (171 journals)
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CHEMICAL ENGINEERING (171 journals)                  1 2     

ACS Combinatorial Science     Full-text available via subscription   (Followers: 9)
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials     Hybrid Journal   (Followers: 4)
Acta Polymerica     Hybrid Journal   (Followers: 6)
Additives for Polymers     Full-text available via subscription   (Followers: 21)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 5)
Advanced Chemical Engineering Research     Open Access   (Followers: 9)
Advanced Powder Technology     Hybrid Journal   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 17)
Advances in Chemical Engineering and Science     Open Access   (Followers: 23)
Advances in Polymer Technology     Hybrid Journal   (Followers: 11)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 5)
Annual Review of Analytical Chemistry     Full-text available via subscription   (Followers: 9)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 10)
Anti-Corrosion Methods and Materials     Hybrid Journal   (Followers: 4)
Applied Petrochemical Research     Open Access   (Followers: 3)
Asia-Pacific Journal of Chemical Engineering     Hybrid Journal   (Followers: 6)
Biochemical Engineering Journal     Hybrid Journal   (Followers: 9)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 5)
BMC Chemical Biology     Open Access   (Followers: 4)
Brazilian Journal of Chemical Engineering     Open Access   (Followers: 2)
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 1)
Carbohydrate Polymers     Hybrid Journal   (Followers: 9)
Catalysts     Open Access   (Followers: 7)
Chemical and Engineering News     Free   (Followers: 4)
Chemical and Materials Engineering     Open Access   (Followers: 1)
Chemical and Petroleum Engineering     Hybrid Journal   (Followers: 9)
Chemical and Process Engineering     Open Access   (Followers: 3)
Chemical and Process Engineering Research     Open Access   (Followers: 5)
Chemical Communications     Full-text available via subscription   (Followers: 30)
Chemical Engineering & Technology     Hybrid Journal   (Followers: 24)
Chemical Engineering and Processing: Process Intensification     Hybrid Journal   (Followers: 10)
Chemical Engineering and Science     Open Access   (Followers: 3)
Chemical Engineering Communications     Hybrid Journal   (Followers: 10)
Chemical Engineering Journal     Hybrid Journal   (Followers: 20)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 16)
Chemical Engineering Research Bulletin     Open Access  
Chemical Engineering Science     Hybrid Journal   (Followers: 13)
Chemical Geology     Hybrid Journal   (Followers: 10)
Chemical Papers     Hybrid Journal   (Followers: 3)
Chemical Product and Process Modeling     Full-text available via subscription   (Followers: 3)
Chemical Reviews     Full-text available via subscription   (Followers: 341)
Chemical Society Reviews     Full-text available via subscription   (Followers: 31)
Chemical Technology     Open Access   (Followers: 5)
ChemInform     Hybrid Journal   (Followers: 3)
Chemistry & Industry     Hybrid Journal   (Followers: 2)
Chemistry Central Journal     Open Access   (Followers: 5)
Chemistry of Materials     Full-text available via subscription   (Followers: 248)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 6)
ChemSusChem     Hybrid Journal   (Followers: 7)
Chinese Chemical Letters     Full-text available via subscription   (Followers: 2)
Chinese Journal of Chemical Engineering     Full-text available via subscription   (Followers: 3)
Coke and Chemistry     Hybrid Journal  
Coloration Technology     Hybrid Journal   (Followers: 1)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 8)
Computer Aided Chemical Engineering     Full-text available via subscription   (Followers: 2)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 7)
CORROSION     Full-text available via subscription   (Followers: 1)
Corrosion Reviews     Full-text available via subscription   (Followers: 4)
Crystal Research and Technology     Hybrid Journal   (Followers: 2)
Current Opinion in Chemical Engineering     Open Access   (Followers: 3)
Education for Chemical Engineers     Hybrid Journal   (Followers: 4)
Ekologia : The Journal of Institute of Landscape Ecology of Slovak Academy of Sciences     Open Access  
Eksergi     Open Access  
Emerging Trends in Chemical Engineering     Full-text available via subscription  
European Polymer Journal     Hybrid Journal   (Followers: 41)
Fibers and Polymers     Full-text available via subscription   (Followers: 3)
Fluorescent Materials     Open Access  
Focusing on Modern Food Industry     Open Access   (Followers: 3)
Frontiers of Chemical Science and Engineering     Hybrid Journal   (Followers: 1)
Geochemistry International     Hybrid Journal  
Handbook of Powder Technology     Full-text available via subscription   (Followers: 2)
Heat Exchangers     Open Access   (Followers: 1)
High Performance Polymers     Hybrid Journal  
Indian Chemical Engineer     Hybrid Journal   (Followers: 3)
Indian Journal of Chemical Technology (IJCT)     Open Access   (Followers: 12)
Industrial & Engineering Chemistry     Full-text available via subscription   (Followers: 9)
Industrial & Engineering Chemistry Research     Full-text available via subscription   (Followers: 19)
Industrial Chemistry Library     Full-text available via subscription   (Followers: 4)
Info Chimie Magazine     Full-text available via subscription   (Followers: 3)
International Journal of Chemical and Petroleum Sciences     Open Access   (Followers: 2)
International Journal of Chemical Engineering     Open Access   (Followers: 7)
International Journal of Chemical Reactor Engineering     Full-text available via subscription   (Followers: 3)
International Journal of Chemical Technology     Open Access   (Followers: 4)
International Journal of Chemoinformatics and Chemical Engineering     Full-text available via subscription   (Followers: 2)
International Journal of Food Science     Open Access   (Followers: 3)
International Journal of Industrial Chemistry     Open Access  
International Journal of Polymeric Materials     Hybrid Journal   (Followers: 3)
International Journal of Science and Engineering     Open Access   (Followers: 7)
International Journal of Waste Resources     Open Access   (Followers: 5)
ISRN Chemical Engineering     Open Access   (Followers: 4)
ISRN Polymer Science     Open Access   (Followers: 11)
Journal of Applied Crystallography     Hybrid Journal   (Followers: 4)
Journal of Applied Electrochemistry     Hybrid Journal   (Followers: 13)
Journal of Applied Polymer Science     Hybrid Journal   (Followers: 219)
Journal of Biomaterials Science, Polymer Edition     Hybrid Journal   (Followers: 8)
Journal of Chemical & Engineering Data     Full-text available via subscription   (Followers: 11)
Journal of Chemical Ecology     Hybrid Journal   (Followers: 2)
Journal of Chemical Engineering     Open Access   (Followers: 4)
Journal of Chemical Engineering and Materials Science     Open Access  
Journal of Chemical Science and Technology     Open Access   (Followers: 3)

        1 2     

Journal Cover   Chemical Engineering Science
  [SJR: 1.033]   [H-I: 103]   [15 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2509
   Published by Elsevier Homepage  [2589 journals]
  • Molecular dynamics as a tool to study heterogeneity in zeolites –
           Effect of Na+ cations on diffusion of CO2 and N2 in Na-ZSM-5
    • Abstract: Publication date: 6 January 2015
      Source:Chemical Engineering Science, Volume 121
      Author(s): David Newsome , Marc-Olivier Coppens
      Zeolites typically contain extra-framework cations to charge-compensate for trivalent Al atom substitutions in the SiO2 framework. These cations, such as Na+, directly interact with quadrupolar guest molecules, such as CO2 and N2, which move through their micropores, causing energetic heterogeneity. To assess the effects of heterogeneity in Na-ZSM-5 on diffusion of CO2 and N2, molecular dynamics (MD) simulations are carried out. In silicalite-1, the pure-silicon form of ZSM-5, the self-diffusivity exhibits a monotonic decrease with molecular loading, while the corrected diffusivity shows a relatively constant value. In contrast, the Na+ cations cause a maximum or a flat profile over molecular loading for the self- and corrected diffusivities of CO2 at T=200 and 300K, while the cations only have minimal impact on the diffusivity of N2. The MD simulations allow us to identify energy basins or sites at which guest molecules spend a relatively long time, and construct a coarse-grained lattice representation for the pore network. Average residence times at these sites are calculated for both species. The trends observed in the residence times correlate to the trends observed in the diffusivity. The residence times for CO2 at T=200K are long at low loading, but decrease with loading as additional CO2 molecules compete to stay close to a cation. In contrast, the residence times for N2 are relatively insensitive to the cations, only mildly increasing near a cation. This difference in behavior can be associated to the quadrupole moments of these molecules.


      PubDate: 2015-02-20T08:04:35Z
       
  • Evaluation of a structural mechanics model to predict the effect of
           inserts in the BEd support of chromatographic columns
    • Abstract: Publication date: Available online 16 February 2015
      Source:Chemical Engineering Science
      Author(s): Spyridon Gerontas , Tian Lan , Martina Micheletti , Nigel J. Titchener-Hooker
      Cell culture titres are expected to increase still further over the forthcoming years. This imposes challenges for downstream processing including the potential need to use larger volumes of chromatography resins. Such a move could create throughput bottlenecks because of the compressible nature of many commercially available resins, which makes the operation of columns with diameters beyond 2m infeasible due to resin collapse. The use of cylindrical inserts of negligible thickness has been proposed in the literature as a way to enhance the level of wall support, allowing higher superficial flow velocities to be applied and hence larger diameter columns to be used. In this study, a structural mechanics model has been developed to evaluate the effect of inserts on the column pressure drop and flow characteristics. Simulations were shown to be in good agreement with published experimental data. The model was then used to predict the effect of insert number, diameter, height and roughness on critical velocity of manufacturing scale columns.


      PubDate: 2015-02-20T08:04:35Z
       
  • Kinetics of the reduction of wüstite by hydrogen and carbon monoxide
           for the chemical looping production of hydrogen
    • Abstract: Publication date: 16 December 2014
      Source:Chemical Engineering Science, Volume 120
      Author(s): Wen Liu , Jin Yang Lim , Marco A. Saucedo , Allan N. Hayhurst , Stuart A. Scott , J.S. Dennis
      Hydrogen of very high purity can be produced via the steam-iron process, in which steam oxidises metallic Fe in 3/4Fe+H2O→1/4Fe3O4+H2. It is then advantageous to oxidise Fe3O4 in air to Fe2O3, an oxygen-carrier. This higher oxide of Fe is then reduced to regenerate metallic iron by reacting with synthesis gas, producing metallic Fe and possibly some wüstite (Fe x O, 0<x<1). In this three-stage process, the reduction of Fe x O to Fe is the slowest reaction. This paper is concerned with the kinetics of the reduction of wüstite (Fe x O) by reaction with CO, and, or H2. Starting with pure (99wt%) wüstite, the intrinsic kinetics of its reduction to metallic iron were measured in fluidised beds at different temperatures. The reaction was found to have 3 distinct stages, (i) the removal of lattice oxygen in wüstite, (ii) rate increasing with conversion of solid and (iii) rate decreasing with conversion of solid. A random pore model was used to simulate the latter stages of the reduction of wüstite by either H2 or CO or a mixture of the two. It was found that the intrinsic rate of reduction in H2 is substantially faster than with CO, whereas the resistances to diffusion of H2 and CO through the product layer of Fe are comparable; these factors account for differences in the overall rates observed with these gases.


      PubDate: 2015-02-05T13:54:02Z
       
  • Numerical simulations of lateral solid mixing in gas-fluidized beds
    • Abstract: Publication date: 16 December 2014
      Source:Chemical Engineering Science, Volume 120
      Author(s): Oyebanjo Oke , Paola Lettieri , Piero Salatino , Roberto Solimene , Luca Mazzei
      We investigated the influence of design parameters and operational conditions on lateral solid mixing in fluidized beds adopting the Eulerian-Eulerian modeling approach. To quantify the rate at which solids mix laterally, we used a lateral dispersion coefficient ( D s r ). Following the usual approach employed in the literature, we defined D s r by means of an equation analogous to Fick׳s law of diffusion. To estimate D s r , we fitted the void-free solid volume fraction radial profiles obtained numerically with those obtained analytically by solving Fick׳s law. The profiles match very well. Our results show that D s r increases as superficial gas velocity and bed height increase; furthermore, it initially increases with bed width, but then remains approximately constant. The values of D s r obtained numerically are larger than the experimental ones, within the same order of magnitude. The overestimation has a twofold explanation. On one side, it reflects the different dimensionality of simulations (2D) as compared with real fluidized beds (3D), which affects the degrees of freedom of particle lateral motion. On the other, it is related to the way frictional solid stress was modeled: we employed the kinetic theory of granular flow model for the frictional solid pressure and the model of Schaeffer (1987) for the frictional solid viscosity. To investigate how sensitive the numerical results are on the constitutive model adopted for the frictional stress, we ran the simulations again using different frictional models and changing the solid volume fraction at which the bed is assumed to enter the frictional flow regime ( ϕ m i n ) . We observed that D s r is quite sensitive to the latter. This is because this threshold value influences the size and behavior of the bubbles in the bed. We obtained the best predictions for ϕ m i n = 0.50 . The results show that accurate prediction of lateral solid dispersion depends on adequate understanding of the frictional flow regime, and accurate modeling of the frictional stress which characterizes it.


      PubDate: 2015-02-05T13:54:02Z
       
  • Prediction of the crystal structures of axitinib, a polymorphic
           pharmaceutical molecule
    • Abstract: Publication date: 6 January 2015
      Source:Chemical Engineering Science, Volume 121
      Author(s): Manolis Vasileiadis , Constantinos C. Pantelides , Claire S. Adjiman
      Organic molecules can crystallize in multiple structures or polymorphs, yielding crystals with very different physical and mechanical properties. The prediction of the polymorphs that may appear in nature is a challenge with great potential benefits for the development of new products and processes. A multistage crystal structure prediction (CSP) methodology is applied to axitinib, a pharmaceutical molecule with significant polymorphism arising from molecular flexibility. The CSP study is focused on those polymorphs with one molecule in the asymmetric unit. The approach successfully identifies all four known polymorphs within this class, as well as a large number of other low-energy structures. The important role of conformational flexibility is highlighted. The performance of the approach is discussed in terms of both the quality of the results and various algorithmic and computational aspects, and some key priorities for further work in this area are identified.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Aggregation of growing crystals in suspension: IIi. accounting for
           adhesion and repulsion
    • Abstract: Publication date: Available online 21 January 2015
      Source:Chemical Engineering Science
      Author(s): K. Pitt , M.J. Hounslow
      In this paper we modify our previously published model describing the aggregation behaviour of crystals growing in suspensions. That model considered aggregation only in terms of cementing, i.e the growth of a neck between colliding particles. In this current work, we introduce into our model the case of aggregation of growing crystals in the presence of inter-particle forces. Here we postulate that aggregation may be augmented by adhesion between the colliding particles, or diminished by repulsion of particles. In the new model we characterise the adhesive or repulsive force by a surface energy acting along a linear contact and subsequently define an adhesion Mumtaz number, M A . In the case of simultaneous cementing and adhesion the Mumtaz number is simply the sum of the separate cementing and adhesion numbers. In this work, two crystallographic forms of calcium oxalate monohydrate (COM) and one form of calcite under both low and high ionic strength conditions were studied. Calcite crystals were found to evidence adhesion between the colliding particles, both a high and low ionic strength. Furthermore, the ionic strength also influenced the cementing parameter. The different forms of COM exhibited both different cementing and inter-particle behaviour. These effects were attributed to differences between the systems at the nano-scale and that aggregation behaviour depends on the anisotropic nature of growing crystals.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Aggregation of growing crystals in suspension: II. Poiseuille flow
           crystalliser
    • Abstract: Publication date: 27 January 2015
      Source:Chemical Engineering Science, Volume 122
      Author(s): Kate Pitt , Michael J. Hounslow
      We describe the design and operation of a Poiseuille Flow Crystalliser (PFC) that allows direct exploration of the effect of hydrodynamic and physico-chemical conditions on the aggregation of crystals growing in suspension. The PFC operates as a differential reactor where changes between inlet and outlet are small enough not to change the rate, but large enough to be measureable. Automatically measured changes in size distribution yield very clear quantitative evidence of aggregation. We use these data to explore the three open questions of Hounslow et al. (2013) and show how to average underlying point aggregation kinetics over a whole vessel and how to extract point data from average data. We introduce the critical aggregate size, D, as the particle size that at the average shear rate has a Mumtaz number, M=1, and so disruptive forces are in balance with the strength of growing bridges. In a study of rounded calcium oxalate monohydrate particles we show that values of D can readily be determined by fitting the change in size distribution in the PFC. We are able to discriminate among candidate models relating aggregation efficiency to M by means of an empirical fitting investigation and by directly determining the aggregation efficiency – both averaged and un-averaged for the vessel. We conclude that aggregate rupture happens under simple tension and that the effective average size of two colliding particles is their geometric mean. D 2 is predicted and observed to be directly proportional to the ratio of crystal growth rate to flow rate squared. We demonstrate that no attractive or repulsive inter-particle forces are active in aiding or retarding aggregation in this system. The constant of proportionality from these results allows the material property controlling aggregation – the product of yield strength and a geometric factor with dimensions of length – to be determined as L ⁎σY=1.35±0.01Nm−1.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Modelling and optimisation of the one-pot, multi-enzymatic synthesis of
           
    • Abstract: Publication date: 27 January 2015
      Source:Chemical Engineering Science, Volume 122
      Author(s): L. Rios-Solis , P. Morris , C. Grant , A.O.O. Odeleye , H.C. Hailes , J.M. Ward , P.A. Dalby , F. Baganz , G.J. Lye
      Advances in synthetic biology are facilitating the de novo design of complex, multi-step enzymatic conversions for industrial organic synthesis. This work describes the integration of multi-step enzymatic pathway construction with enzyme kinetics and bioreactor modelling, in order to optimise the synthesis of chiral amino-alcohols using engineered Escherichia coli transketolases (TK) and the Chromobacterium violaceum transaminase (TAm). The specific target products were (2S,3S)-2-aminopentane-1,3-diol (APD) and (2S,3R)-2-amino-1,3,4-butanetriol (ABT). Kinetic models and parameters for each of the enzymatic steps were first obtained using automated microwell experiments. These identified the TK-catalysed conversions as being up to 25 times faster than the subsequent TAm conversions and inhibition of TAm by the amino-donor used, (S)-(−)-α-methylbenzylamine (MBA), as limiting the overall conversion yields. In order to better ‘match’ the relative rates of the two enzymes an E. coli expression system, based on two compatible plasmids, was constructed to produce both enzymes in a single host. By control of induction time and temperature it was possible to produce six times more recombinant TAm than TK to help balance the reaction rates. To overcome MBA inhibition and an unfavourable reaction equilibrium, fed-batch addition of the amino-donor was introduced as well as the use of isopropylamine as an alternate amino-donor. Adopting these strategies, and using the kinetic models to optimise feeding strategies, the one pot syntheses of APD and ABT were successfully scaled-up to preparative scales. Excellent agreement was found between the kinetic profiles and yields predicted and those achieved experimentally at the larger scale. In this case the integration of these multi-disciplinary approaches enabled us to achieve up to a 6 fold greater yield using concentrations an order of magnitude higher than in previous preparative scale batch bioconversions carried out sequentially.


      PubDate: 2015-02-05T13:54:02Z
       
  • A comparison of magnetic resonance, X-ray and positron emission particle
           tracking measurements of a single jet of gas entering a bed of particles
    • Abstract: Publication date: 27 January 2015
      Source:Chemical Engineering Science, Volume 122
      Author(s): M. Pore , G.H. Ong , C.M. Boyce , M. Materazzi , J. Gargiuli , T. Leadbeater , A.J. Sederman , J.S. Dennis , D.J. Holland , A. Ingram , P. Lettieri , D.J. Parker
      Measurements of the lengths of a single jet of gas entering a packed bed were made using magnetic resonance imaging (MRI), positron emission particle tracking (PEPT) and X-ray radiography and the results compared. The experiments were performed using a Perspex bed (50mm i.d.) of poppy seeds: air at 298K was admitted to the base of the bed through a single, central orifice, 2mm in diameter. Poppy seeds (Geldart Group B, measured minimum fluidisation velocity with air at 298K and 1atm of 0.13m/s and particle density ~1060kg/m3) were used because of their high content of oil, which contains mobile protons and hence is suitable for MRI examination. The lengths of jet measured using the three techniques were in agreement between 50m/s<U o <100m/s, where U o is the superficial velocity through the orifice. Below U o =50m/s, X-ray measurements of jet lengths were shorter than those measured using MRI. This was attributed to the minimum diameter of void, found to be 5mm, detectable in a 50mm bed using ultra-fast X-ray measurements. PEPT is most commonly used to calculate particle velocities, whilst jet lengths are usually calculated from determinations of voidage. However, the particle locations determined in this work by PEPT were used to calculate a fractional occupancy count, from which a jet length could be inferred.


      PubDate: 2015-02-05T13:54:02Z
       
  • Analysis of the Cyanobacterial Hydrogen Photo-Production Process via Model
           Identification and Process Simulation
    • Abstract: Publication date: Available online 2 February 2015
      Source:Chemical Engineering Science
      Author(s): Dongda Zhang , Pongsathorn Dechatiwongse , Ehecatl Antonio Del-Rio-Chanona , Klaus Hellgardt , Geoffrey.C. Maitland , Vassilios.S. Vassiliadis
      Cyanothece sp. ATCC 51142 is considered a microorganism with the potential to generate sustainable hydrogen in the future. However, few kinetic models are capable of simulating different phases of Cyanothece sp. ATCC 51142 from growth to hydrogen production. In the present study four models are constructed to simulate Cyanothece sp. batch photoproduction process. A dynamic optimisation method is used to determine parameters in the models. It is found that although the piecewise models fit experimental data better, large deviation can be induced when they are used to simulate a process whose operating conditions are different from the current experiments. The modified models are eventually selected in the present study to simulate a two-stage continuous photoproduction process. The current simulation results show that a plug flow reactor (PFR) shows worse performance compared to a continuous stirred-tank reactor (CSTR) in the current operating conditions since its lower the total hydrogen production. The finding is that nitrate and oxygen concentration change along the direction of culture movement in PFR, and hydrogen is only generated in the zone where both of them are low. The reactor area thereby is not well utilised. Additionally, as the hydrogen production rate is primarily influenced by biomass concentration, which increases initially and decreases eventually along the direction of culture movement, the overall hydrogen production rate in a PFR may be lower than that in a CSTR. Finally, in this study fed-batch photoproduction processes are proposed containing only one photobioreactor based on the current simulation.


      PubDate: 2015-02-05T13:54:02Z
       
  • Partial oxidation of methane using silver/gadolinia-doped ceria composite
           membranes
    • Abstract: Publication date: Available online 2 February 2015
      Source:Chemical Engineering Science
      Author(s): E. Ruiz-Trejo , P. Boldrin , J.L. Medley-Hallam , J. Darr , A. Atkinson , N.P. Brandon
      Methane was partially oxidised to CO using oxygen permeated through a 1-mm thick silver/Ce0.9Gd0.1O2−x (Ag/CGO) composite membrane operating at 500–700°C with air at 1bar pressure. The membranes were fabricated by sintering ultrafine nanoparticles of gadolinia-doped ceria (<5nm) coated with silver using Tollens' reaction. This unique combination led to dense composites with low content of silver (7vol %), no reaction between the components and predominant metallic conductivity. When feeding 4% methane at 700°C to a 1-mm thick Ag/CGO using Ni as reforming catalyst, the conversion reached 21% and the CO selectivity 92% with an estimated oxygen flux of 0.18mLmin−1 cm−2 (NTP). The samples were stable in carbon-containing atmospheres and under a large pO2 transmembrane pressure difference at temperatures below 700°C for 48h.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Numerical analysis of strain rate sensitivity in ball indentation on
           cohesive powder Beds
    • Abstract: Publication date: 17 February 2015
      Source:Chemical Engineering Science, Volume 123
      Author(s): M. Pasha , C. Hare , A. Hassanpour , M. Ghadiri
      In the shear deformation of powder beds beyond the quasi-static regime the shear stress is dependent on the strain rate. Extensive work has been reported on the rapid chute flow of large granules but the intermediate regime has not been widely addressed particularly in the case of cohesive powders. However in industrial powder processes the powder flow is often in the intermediate regime. In the present work an attempt is made to investigate the sensitivity of the stresses in an assembly of cohesive spherical particles to the strain rate in ball indentation using the Distinct Element Method. This technique has recently been proposed as a quick and easy way to assess the flowability of cohesive powders. It is shown that the hardness, deviatoric and hydrostatic stresses within a bed, subjected to ball indentation on its free surface, are dependent on the indentation strain rate. These stresses are almost constant up to a dimensionless strain rate of unity, consistent with trends from traditional methods of shear cell testing, though fluctuations begin to increase from a dimensionless strain rate of 0.5. For dimensionless strain rates greater than unity, these stresses increase, with the increase in hardness being the most substantial. These trends correlate well with those established in the literature for the Couette device. However the quantitative value of the strain rate boundary of the regimes differs, due to differences in the geometry of shear deformation bands. Nevertheless, this shows the capability of the indentation technique in capturing the dynamics of cohesive powder flow.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Measurement of bubble sizes in fluidised beds using electrical capacitance
           tomography
    • Abstract: Publication date: 14 April 2015
      Source:Chemical Engineering Science, Volume 126
      Author(s): T.C. Chandrasekera , Y. Li , D. Moody , M.A. Schnellmann , J.S. Dennis , D.J. Holland
      Electrical capacitance tomography (ECT) provides a means for non-invasively imaging multiphase flows, such as those in fluidised beds. Traditionally ECT images are reconstructed using the assumption that the distribution of permittivity varies smoothly throughout the sensor region. However, for many applications there are step changes in the permittivity, for example, between the bubble and particulate phases in a fluidised bed, and the assumption of smoothness is flawed. In this article a Total Variation Iterative Soft Thresholding (TV-IST) algorithm is used to reconstruct ECT images that allows for sharp transitions in the permittivity distribution. This new algorithm has been compared with established algorithms for ECT image reconstruction. It was found that the TV-IST algorithm reduced the sensitivity to the threshold level chosen when extracting measurements of bubble size from ECT data sets. Measurements of the bubble size distribution in the fluidised bed using the TV-IST algorithm agreed closely with established empirical correlations for the size of bubbles. The results demonstrate that ECT can provide accurate and high spatial resolution measurements of features such as bubbles in gas-solid fluidised beds.


      PubDate: 2015-02-05T13:54:02Z
       
  • An investigation on the mechanics of homogeneous expansion in
           gas-fluidized beds
    • Abstract: Publication date: 4 May 2015
      Source:Chemical Engineering Science, Volume 127
      Author(s): Oyebanjo Oke , Paola Lettieri , Luca Mazzei
      The Richardson and Zaki (1954, Sedimentation and fluidization. Trans. Inst. Chem. Eng. 32, pp. 35–53.) equation has been used extensively to investigate the expansion profiles of homogeneous gas-fluidized beds. The experimental value of the parameter n appearing in the equation indicates how significantly interparticle forces affect the expansion of these beds, revealing the relative importance of these forces with respect to the fluid dynamic ones. In this work, we modeled the stable expansion of gas-fluidized beds of different diameter, accounting for enduring contacts among particles and wall effects. We solved the model numerically to obtain the bed expansion profiles, back-calculating from them the values of the parameter n. For all the cases considered, we observed that the values of n are higher than those obtained by purely fluid dynamic correlations, such as those advanced by Richardson and Zaki, and Rowe (1987, A convenient empirical equation for estimation of the Richardson and Zaki exponent. Chem. Eng. Sci. 42, pp. 2795.). This effect was more pronounced in beds of smaller diameter. To validate our model, we carried out fluidization and defluidization experiments, analyzing the results by means of the Richardson and Zaki equation. We obtained a reasonable agreement between numerical and experimental findings; this suggests that enduring contacts among particles, which are manifestations of cohesiveness, affect homogeneous bed expansion. This effect is amplified by wall friction.


      PubDate: 2015-02-05T13:54:02Z
       
  • Predictive simulation of nanoparticle precipitation based on the
           population balance equation
    • Abstract: Publication date: January 2006
      Source:Chemical Engineering Science, Volume 61, Issue 1
      Author(s): Hans-Christoph Schwarzer , Florian Schwertfirm , Michael Manhart , Hans-Joachim Schmid , Wolfgang Peukert
      Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulation with a Lagrangian particle tracking strategy is applied in combination with the coupled population balance–micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation.


      PubDate: 2015-02-05T13:54:02Z
       
  • Incremental identification of kinetic models for homogeneous reaction
           systems
    • Abstract: Publication date: August 2006
      Source:Chemical Engineering Science, Volume 61, Issue 16
      Author(s): Marc Brendel , Dominique Bonvin , Wolfgang Marquardt
      An incremental approach for the identification of stoichiometries and kinetics of complex homogeneous reaction systems is presented in this paper. The identification problem is decomposed into a sequence of subproblems. First, the reaction fluxes for the various species are estimated on the basis of balance equations and concentration measurements stemming from isothermal experiments. This task represents an ill-posed inverse problem that requires appropriate regularization. Using target factor analysis, suitable reaction stoichiometries can then be identified. In a further step, the reaction rates are estimated without postulating a kinetic structure. Finally, the kinetic laws, i.e., the dependencies of the reaction rates on concentrations, are constructed by selecting the best model structure from a set of model candidates. This incremental approach is shown to be both efficient and flexible for utilizing the available process knowledge. The methodology is illustrated on the industrially relevant acetoacetylation of pyrrole with diketene.


      PubDate: 2015-02-05T13:54:02Z
       
  • Theoretical performance of countercurrent reactors for production of
           enantiopure compounds
    • Abstract: Publication date: 1 February 2011
      Source:Chemical Engineering Science, Volume 66, Issue 3
      Author(s): Marija Saric , Luuk A.M. van der Wielen , Adrie J.J. Straathof
      Irreversible reactions are being applied in enzymatic kinetic resolution to obtain enantiomerically pure compounds from racemic mixtures. Using model calculations for situations without mass transfer limitation, we show that reversible reactions might also be useful for enzymatic kinetic resolution, provided that countercurrent systems are used rather than batch or cocurrent systems. The required reaction time or enzyme amount in a countercurrent system is much lower than in an analogous cocurrent system or its batch equivalent. More importantly, often the calculated yield and enantiomeric excess are better in countercurrent systems. Racemization can also be favorably used in countercurrent systems. Consequently, to achieve with a reversible reaction a particular enantiomeric excess and yield, a countercurrent system needs less dilution or activated co-reactant and less enantioselective enzyme than a cocurrent system.


      PubDate: 2015-02-05T13:54:02Z
       
  • Designing control system with entropic modeling
    • Abstract: Publication date: 1 February 2011
      Source:Chemical Engineering Science, Volume 66, Issue 3
      Author(s): J. Manzi , R. Brito , H. Bispo
      Contributions of entropic modeling to the performance of reactive process control have been investigated. Modeling has been developed based on mass, energy and entropy balances and thermodynamic relations, resulting in a model for the entropy production rate. Using the conventional optimization technique, a minimum for the entropy production rate was found when a given relationship between the temperatures of the inlet stream and of the reaction is satisfied for a particular residence time in the reactor. A new class of nonlinear controller is proposed by means of introducing entropic models into the classical algorithms designed from a synthesis of the reference system. The results indicate that such a controller yields a superior performance when compared with classical feedback control strategies.


      PubDate: 2015-02-05T13:54:02Z
       
  • Preparation and CO2 adsorption of amine modified Mg–Al LDH via
           exfoliation route
    • Abstract: Publication date: 22 January 2012
      Source:Chemical Engineering Science, Volume 68, Issue 1
      Author(s): Jiawei Wang , Lee A. Stevens , Trevor C. Drage , Joe Wood
      In response to the recent focus on reducing carbon dioxide emission, the preparation and characterization of organically functionalized materials for use in carbon capture have received considerable attention. In this paper the synthesis of amine modified layered double hydroxides (LDHs) via an exfoliation and grafting synthetic route is reported. The materials were characterized by elemental analysis (EA), powder x-ray diffraction (PXRD), diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) and thermogravimetric analysis (TGA). Adsorption of carbon dioxide on modified layered double hydroxides was investigated by TGA at 25–80°C. 3-[2-(2-Aminoethylamino) ethylamino]propyl-trimethoxysilane modified MgAl LDH showed a maximum CO2 adsorption capacity of 1.76mmolg−1 at 80°C. The influence of primary and secondary amines on carbon dioxide adsorption is discussed. The carbon dioxide adsorption isotherms presented were closely fitted to the Avrami kinetic model.
      Highlights . ► Amine modified layered double hydroxides were prepared via exfoliation and grafting route. ► CO2 adsorption was studied at 25–80°C and 1bar CO2 pressure. ► Highest CO2 adsorption capacity of 1.75mmolg−1 was achieved at 80°C. ► The Avrami model provided a good fit to the CO2 adsorption isotherms.

      PubDate: 2015-02-05T13:54:02Z
       
  • Synthesis, crystallization and characterization of diastereomeric salts
           formed by ephedrine and malic acid in water
    • Abstract: Publication date: 30 July 2012
      Source:Chemical Engineering Science, Volume 77
      Author(s): Han Wu , Anthony R. West , Martin Vickers , David C. Apperley , Alan G. Jones
      A screening of crystallization conditions for the diastereomeric salts formed by L/D-malic acid and a common resolving agent, L-Ephedrine, in water is reported. So far, 7 different forms of salts with 1:1 and 2:1 stoichiometries were successfully crystallized, including one previously reported 1:1 LL salt. All new salts were characterized by differential scanning calorimetry, thermogravimetric and elemental analysis, infrared spectroscopy, solid-state NMR and powder XRD. 1:1 stoichiometry favours anhydrate formation while 2:1 stoichiometry tends to give monohydrate forms. Two monohydrates dehydrate on heating to produce anhydrous salts. A 2:1 LD trihydrate was discovered by vapor sorption experiments and is stable only at high relative humidity (>50%). Differences in stoichiometry and hydrate formation during salt crystallization, leading to differences in physicochemical properties could have a significant impact on resolution conditions and outcome.
      Graphical abstract image Highlights ► Discovery of a simple system consisting of 7 different salt forms of L-Eph. ► Successful salt screening by dry/wet grinding and RH controlled crystallization. ► 1:1 stoichiometry favours anhydrate formation. ► 2:1 stoichiometry tends to give monohydrate forms. ► 2:1 LD trihydrate is stable only at high relative humidity (>50%).

      PubDate: 2015-02-05T13:54:02Z
       
  • Two-phase air–water flow through a large diameter vertical 180o
           return bend
    • Abstract: Publication date: 10 September 2012
      Source:Chemical Engineering Science, Volume 79
      Author(s): M. Abdulkadir , D. Zhao , A. Azzi , I.S. Lowndes , B.J. Azzopardi
      An experimental study of churn-annular flow behaviour and mean film fraction of an air–water mixture flowing through a vertical 180° return bend using an electrical conductance technique is reported. Measurements were made of film fraction using probes placed before, within the bend (45o, 90o, 135o) and after the bend. The bend, made of transparent acrylic resin, has a diameter of 127mm and a curvature ratio (R/D) of 3. The superficial velocities of air ranged from 3.5 to 16.1m/s and those for water from 0.02 to 0.2m/s. Flow patterns were identified using the characteristic signatures of Probability Density Function (PDF) plots of the time series of mean film fraction. The average film fraction is identified to be higher in the straight pipes than in the bends. The study also identified that at low gas superficial velocity, the film fraction for the riser was generally greater than for the downcomer. For low liquid and higher gas flow rates, film break down occurs at the 45o bend due to gravity drainage. The condition for which the liquid goes to the outside or inside of the bend are identified based on a modified form of Froude number based on published material. A comparison between the present work and that of Hills (1973) based on the mean film fraction showed same tendency.
      Highlights ► Large scale experiments on gas/liquid flow inverted U bend geometry. ► Time series of fraction of liquid travelling as film. ► Flow pattern identification. ► Criterion for identifying whether liquid on inside and outside of bend.

      PubDate: 2015-02-05T13:54:02Z
       
  • Mixing patterns in water plugs during water/ionic liquid segmented flow in
           microchannels
    • Abstract: Publication date: 1 October 2012
      Source:Chemical Engineering Science, Volume 80
      Author(s): Valentina Dore , Dimitrios Tsaoulidis , Panagiota Angeli
      Circulation patterns and mixing characteristics within water plugs in liquid/liquid segmented flow were investigated by means of micro-Particle Image Velocimetry. Experiments were carried out in a glass microchannel with circular cross-section of 100μm radius using [C4mim][NTf2] ionic liquid as the carrier fluid. A T-junction was used as inlet, while mixture velocities varied from 0.0028m/s to 0.0674m/s. Two main circulation vortices were found within the plugs while at intermediate mixture velocities two additional secondary vortices appeared at the plug front. The mixing rate was locally quantified by means of the non-dimensional circulation time, which was calculated across the plug length. Consistently with the circulation patterns, the non-dimensional circulation time was found to have a profile along the direction of the flow that mirrors the shape of the plug, with a minimum at the axial location of the vortex cores (where the circulation velocity is maximum at the channel centre) while it tended to infinity towards the liquid/liquid interfaces. For all the experiments the minimum value of the circulation time fell within the range of 1.00–1.75. For increasing mixture velocities (i.e. increasing Ca) and sufficiently long plugs (ε IL=0.4) a general decrease (i.e. higher mixing rate) of the circulation time minimum was found, although the behaviour was rather complex. On the other hand, the circulation velocity linearly increased as the Ca number (mixture velocity) increased.
      Highlights ► Plug flow in microchannels using ionic liquid. ► Image analysis to obtain PIV velocity maps and plug characteristics. ► Secondary vortices found in plugs at medium mixture velocities. ► New correlation for film thickness. ► Circulation time profiles depend on mixing velocity and plug length.

      PubDate: 2015-02-05T13:54:02Z
       
  • Effect of bud scars on the mechanical properties of Saccharomyces
           cerevisiae cell walls
    • Abstract: Publication date: 24 December 2012
      Source:Chemical Engineering Science, Volume 84
      Author(s): R.D. Chaudhari , J.D. Stenson , T.W. Overton , C.R. Thomas
      To determine the effect of bud scars on the mechanical properties of the walls of Saccharomyces cerevisiae cells, freshly cultivated stationary phase cells stained with Alexa Fluor 488 conjugated wheat germ agglutinin were sorted according to the number of bud scars using fluorescence-activated cell sorting (FACS). The groups were daughter cells with no bud scars, and mother cells separated further by number of scars (one, two and more than two). Cells with more than three scars were very rare. Compression testing by micromanipulation was used to determine key mechanical properties of the sorted cells. For all cells the force and fractional deformation at bursting could be determined. For 69% of cells overall but only 32% of daughter cells, a large strain mathematical model using a linear elastic constitutive equation for the wall material could be fitted to force deformation data up to cell wall failure. For these cells, the wall surface modulus, elastic modulus, initial stretch ratio and strain energy per unit volume at bursting could be estimated. For the remainder of the cells, the lack of permanent deformation on repeated compression and release (at deformations not causing bursting) suggested the cell wall material was non-linear elastic but with no observable plastic behaviour. This is the first report to show directly that bud scars affect the global mechanical properties of yeast cells and that the important distinction with respect to scars is between daughter and mother cells. The former were smaller with more elastic walls and a higher mean initial stretch ratio. For cells for which the model could be fitted, the mean circumferential strain at bursting decreased with scarring (consistent with stiffer walls) whilst the stress increased. This may be due to the reported absence of chitin in the walls of daughter cells.
      Highlights ▸ Freshly grown S. cerevisiae cells were sorted by number of bud scars using FACS. ▸ Mechanical properties of the sorted cells were found by compression testing. ▸ 69% of cell walls were linear elastic to bursting but only 32% of daughter cells. ▸ Scars caused mechanical property differences between daughter and mother cells.

      PubDate: 2015-02-05T13:54:02Z
       
  • Effect of surface energy on the transition from fixed to bubbling
           gas-fluidised beds
    • Abstract: Publication date: 7 March 2013
      Source:Chemical Engineering Science, Volume 90
      Author(s): Fang Yang , Colin Thornton , Jonathan Seville
      Two-dimensional DEM–CFD simulations have been performed in order to examine the effect of surface energy on the transitional behaviour from fixed bed to bubbling bed for Geldart Type A particles. The results of the simulations presented in the paper show that any effect of surface energy on the magnitude of U mf is not due to increasing bed resistance as a result of increasing the interparticle bond strength. It is demonstrated that U mf corresponds to a deterministic (isostatic) state that is in effect the initiation of the transition from solid-like to fluid-like behaviour. It is also shown that the so-called ‘homogeneous expansion' regime is not in fact homogeneous. This is because the system, when U>U mf , consists of agglomerates. Consequently, the idea that bed expansion is due to the ‘elasticity’ of the bed is not tenable. In order to break up the agglomerates and create a fully fluidised bed that will allow bubbling to occur, higher superficial gas velocities are required for higher values of surface energy. Once the bed is fully fluidised and bubbling occurs the effect of surface energy becomes insignificant.
      Highlights ▸ U mf is an isostatic state that is the transition to fluid-like behaviour. ▸ The so-called ‘homogeneous expansion’ regime is not in fact homogeneous. ▸ The idea that bed expansion is due to the ‘elasticity’ of the bed is not tenable.

      PubDate: 2015-02-05T13:54:02Z
       
  • Investigation of factors affecting isolation of needle-shaped particles in
           a vacuum-agitated filter drier through non-invasive measurements by Raman
           spectrometry
    • Abstract: Publication date: 20 September 2013
      Source:Chemical Engineering Science, Volume 101
      Author(s): Peter Hamilton , David Littlejohn , Alison Nordon , Jan Sefcik , Paul Slavin , John Andrews , Paul Dallin
      The effects of pressure filtration and vacuum agitated drying on cellobiose octaacetate (COA) particles in methanol slurries were studied by making Raman measurements through the glass wall at the side of a filter drier beneath the oil jacket. The change in intensity of methanol peaks in the spectra allowed the removal of the solvent from the particle bed to be monitored. Also, drying curves for COA generated from the Raman measurements gave an indication of the changing physical status of the particle bed during continuous or intermittent agitation. The intensity of the Raman signal for COA depended on the bulk density of the particle bed, which changed due to aggregation and attrition that occurred during solvent removal and particle motion induced by agitation during vacuum drying. Loss on drying (LOD) measurements of samples removed at the end of the pressure filtration and vacuum agitated drying stages established the degree of wetness and confirmed the end point of drying (<0.5% w/w solvent), respectively. Dynamic image analysis confirmed that minimum attrition of COA was achieved when (a) the majority of the methanol was removed during pressure filtration at 0.5bar N2 and (b) intermittent agitation was applied during the vacuum drying stage.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Evaporation dynamics of microbubbles
    • Abstract: Publication date: 20 September 2013
      Source:Chemical Engineering Science, Volume 101
      Author(s): William B. Zimmerman , Mahmood K.H. Al-Mashhadani , H.C. Hemaka Bandulasena
      Until recently, generating clouds of microbubbles was a relatively expensive proposition, with the smallest bubbles requiring high energy density from either the saturation–nucleation mechanism or Venturi effect. Due to the expense of processing with microbubbles, exploration of the acceleration effects of microbubbles for physico-chemical processes are largely unstudied, particularly those that are combined effects. In this paper, the trade-off between heat transfer and evaporation on the microbubble interface are explored, largely by computational modelling but supported by some experimental evidence. The hypothesis is that both processes are inherently transient, but that during short residence times, vaporization is favoured, while at longer residence times, sensible heat transfer dominates and results in re-condensation of the initially vaporized liquid. The computational model address how thin a layer thickness will result in the maximum absolute vaporization, after which sensible heat transfer condenses the vapour as the bubble cools. This maximum vaporization layer thickness is estimated to be a few hundred microns, on the order of a few microbubble diameters at most. If the maximum vaporization estimate and the contact time necessary to achieve it are accurately estimated, these are engineering design features needed to design a vaporizing system to achieve maximum removal of vapour with minimum heat transfer. The modelling work presented here should be considered in light of the humidification experiments also conducted which showed the exit air at 100% saturation, but increasing gas temperature with decreasing layer height, and decreasing water temperature with decreasing layer height, all of which are consistent with the predictions of the computational model.


      PubDate: 2015-02-05T13:54:02Z
       
  • Solubility of carbon dioxide in aqueous blends of
           2-amino-2-methyl-1-propanol and piperazine
    • Abstract: Publication date: 20 September 2013
      Source:Chemical Engineering Science, Volume 101
      Author(s): Danlu Tong , Geoffrey C. Maitland , Martin J.P. Trusler , Paul S. Fennell
      In this work, we report new solubility data for carbon dioxide in aqueous blends of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). A static-analytical apparatus, validated in previous work, was employed to obtain the results at temperatures of (313.2, 333.2, 373.2, 393.2)K, and at total pressures up to 460kPa. Two different solvent blends were studied, both having a total amine mass fraction of 30%: (25 mass% AMP+5 mass% PZ) and (20 mass% AMP+10 mass% PZ). Comparisons between these PZ activated aqueous AMP systems and 30 mass% aqueous AMP have been made in terms of their cyclic capacities under typical scrubbing conditions of 313K in the absorber and 393K in the stripper. The Kent–Eisenberg model was used to correlate the experimental data.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Segregation dynamics of dense polydisperse fluidized suspensions modeled
           using a novel formulation of the direct quadrature method of moments
    • Abstract: Publication date: 20 September 2013
      Source:Chemical Engineering Science, Volume 101
      Author(s): Luca Mazzei
      Computational fluid dynamics (CFD) may be a useful design tool, provided that the mathematical models that we solve with it capture and describe well the most important features of the systems of interest. For fluidized beds, one of these features is the polydispersity of the powders: particles differ in size and alter their size distribution in time and space continuously. To model this key phenomenon, one needs to solve a population balance equation, that is, an equation that governs the evolution of the size distribution. The direct quadrature method of moments (DQMOM) allows doing so in commercial CFD codes at relatively low computational cost. This technique, successfully employed for describing dilute multiphase flows of particles that share the same velocity, still needs testing in the context of dense multiphase flows. Dense polydisperse fluidized powders can segregate or mix, depending on the process operating conditions, and to describe these phenomena one needs to let particles move with different velocities. In this work we use a recent version of DQMOM that has this feature: each quadrature class is advected with its own velocity. The transport equations of this model feature a diffusive-like contribution that allows the powders to mix at the particle length scale. We discuss how to assign a value to the diffusion coefficient and we carry out a sensitivity analysis on the latter; to do so, we simulate the mixing of powders initially segregated using different values for the diffusivity. Successively, after having estimated a suitable value for the latter, we simulate the system dynamics under conditions that should promote segregation, validating the results of the simulations experimentally.


      PubDate: 2015-02-05T13:54:02Z
       
  • CFD simulation of bubbling fluidized bidisperse mixtures: Effect of
           integration methods and restitution coefficient
    • Abstract: Publication date: 11 October 2013
      Source:Chemical Engineering Science, Volume 102
      Author(s): C. Tagliaferri , L. Mazzei , P. Lettieri , A. Marzocchella , G. Olivieri , P. Salatino
      In this work we simulated the dynamics of a fluidized bed of a binary solid mixture using the isothermal multi-fluid model of the commercial CFD code Fluent 12. We focused the attention on the role of both restitution coefficient and integration methods on the dynamics of the bed, adopting a mixture of solids assorted in size (with constant density) as case study. We employed two methods of spatial discretization: first-order upwind scheme (FUS) and second-order upwind scheme (SUS). We investigated implicit versus explicit time integration methods as well. The numerical diffusion introduced by the FUS resulted in a low bubble fraction in the bed, in turn reducing solid mixing rates. Simulations carried out adopting the SUS were characterized by a reasonable bubble fraction and associated solid mixing rate. The latter method successfully predicted the transition to fully mixed, uniform fluidization conditions. The value of the restitution coefficient did not significantly affect the results of the simulations, as bubble volume fraction and jetsam concentration profiles did not show any significant change within the interval of restitution coefficient values investigated, with the exception of the nearly ideal value of 0.99.


      PubDate: 2015-02-05T13:54:02Z
       
  • Achieving ultra-high platinum utilization via optimization of PEM fuel
           cell cathode catalyst layer microstructure
    • Abstract: Publication date: 11 October 2013
      Source:Chemical Engineering Science, Volume 102
      Author(s): J. Marquis , M.-O. Coppens
      Inefficient usage of expensive platinum catalyst has plagued the design of PEM fuel cells and contributed to the limited production and use of fuel cell systems. Here, it is shown that hierarchical optimization can increase platinum utilization 30-fold over existing catalyst layer designs while maintaining power densities over 0.35W/cm2. The cathode catalyst layer microstructure is optimized with respect to platinum utilization (measured as kilowatts of electricity produced per gram of platinum). A one-dimensional agglomerate model that accounts for liquid water saturation is used in this study. The cathode catalyst layer microstructure is optimized by manipulating the platinum loading (m Pt ), platinum-to-carbon ratio (Pt C), and catalyst layer void fraction ( ε V c l ) . The resulting catalyst layer microstructure features ultra-low platinum loadings of roughly 0.01mg/cm2.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
  • Macroscopic multi-dimensional modelling of electrochemically promoted
           systems
    • Abstract: Publication date: 18 December 2013
      Source:Chemical Engineering Science, Volume 104
      Author(s): I.S. Fragkopoulos , I. Bonis , C. Theodoropoulos
      The objective of this work is the construction of macroscopic models for electrochemically promoted catalytic systems, i.e. systems where the catalytic performance is improved by application of potential between the anode and cathode electrodes in the cell. This polarization effect leads to a formation of an effective double layer over the catalytic film due to migration of ‘backspillover’ species from the electrolyte to the working electrode when potential difference is applied in the system. In this paper, we propose a multidimensional, isothermal, dynamic solid oxide single pellet model, which describes the chemical and electrochemical phenomena taking place under polarization conditions. The electrochemically promoted oxidation of CO over Pt/YSZ is used as an illustrative system. The partial differential equation-based 2- and 3-dimensional macroscopic models that describe the simultaneous mass and charge transport in the pellet are constructed and solved in COMSOL Multiphysics. The model predicts species coverage on the catalytic surface, electronic and ionic potential curves across the pellet, gas mixture concentration within the reactor and CO2 production rate. Parameter estimation is undertaken so as to provide us with values of parameters, which are necessary for the simulation of the model. Subsequent sensitivity analysis is performed to investigate the effect of the percentage change of each estimated parameter on the CO2 production rate. As it is shown, the reaction rate curves obtained from the current modelling framework are in good agreement with values found in the literature.


      PubDate: 2015-02-05T13:54:02Z
       
  • Utilizing a highly responsive gene, yhjX, in E. coli based production of
           1,4-butanediol
    • Abstract: Publication date: 15 November 2013
      Source:Chemical Engineering Science, Volume 103
      Author(s): Heather L Szmidt-Middleton , Mario Ouellet , Paul D Adams , Jay D Keasling , Aindrila Mukhopadhyay
      The role of yhjX, a predicted major facilitator superfamily protein, was examined in context of E. coli response to 1,4-butanediol (1,4-BDO). E. coli DH1 and MG1655, two commonly used metabolic engineering hosts, were both sensitive to the presence of 1,4-BDO in the growth medium, but to different extents. The strains also showed differences in the transcriptional response of the yhjX gene that was highly induced in response to 1,4-BDO. yhjX deletion improved growth of the E. coli strains in the control defined medium but did not significantly impact 1,4-BDO sensitivity. Overexpression of yhjX using a plasmid-borne copy and lactose-inducible promoter also did not result in an improvement in 1,4-BDO tolerance. However, the large differential expression of yhjX in response to this diol provided the foundation to develop a biosensor for the detection of 1,4-BDO using a fluorescent gene under the control of the yhjX promoter. A basic P yhjX :GFP biosensor in E. coli DH1 allows the detection of 4–7% 1,4-BDO in the extracellular medium and provides a tool for high throughput engineering for improving 1,4-BDO production strains.


      PubDate: 2015-02-05T13:54:02Z
       
  • On the fluid dynamics of a laboratory scale single-use stirred bioreactor
    • Abstract: Publication date: 24 May 2014
      Source:Chemical Engineering Science, Volume 111
      Author(s): A.O.O. Odeleye , D.T.J. Marsh , M.D. Osborne , G.J. Lye , M. Micheletti
      The commercial success of mammalian cell-derived recombinant proteins has fostered an increase in demand for novel single-use bioreactor (SUB) systems that facilitate greater productivity, increased flexibility and reduced costs (Zhang et al., 2010). These systems exhibit fluid flow regimes unlike those encountered in traditional glass/stainless steel bioreactors because of the way in which they are designed. With such disparate hydrodynamic environments between SUBs currently on the market, traditional scale-up approaches applied to stirred tanks should be revised. One such SUB is the Mobius® 3L CellReady, which consists of an upward-pumping marine scoping impeller. This work represents the first experimental study of the flow within the CellReady using a Particle Image Velocimetry (PIV) approach, combined with a biological study into the impact of these fluid dynamic characteristics on cell culture performance. The PIV study was conducted within the actual vessel, rather than using a purpose-built mimic. PIV measurements conveyed a degree of fluid compartmentalisation resulting from the up-pumping impeller. Both impeller tip speed and fluid working volume had an impact upon the fluid velocities and spatial distribution of turbulence within the vessel. Cell cultures were conducted using the GS-CHO cell-line (Lonza) producing an IgG4 antibody. Disparity in cellular growth and viability throughout the range of operating conditions used (80–350rpm and 1–2.4L working volume) was not substantial, although a significant reduction in recombinant protein productivity was found at 350rpm and 1L working volume (corresponding to the highest Reynolds number tested in this work). The study shows promise in the use of PIV to improve understanding of the hydrodynamic environment within individual SUBs and allows identification of the critical hydrodynamic parameters under the different flow regimes for compatibility and scalability across the range of bioreactor platforms.


      PubDate: 2015-02-05T13:54:02Z
       
  • Assessment of different methods of analysis to characterise the mixing of
           shear-thinning fluids in a Kenics KM static mixer using PLIF
    • Abstract: Publication date: 14 June 2014
      Source:Chemical Engineering Science, Volume 112
      Author(s): F. Alberini , M.J.H. Simmons , A. Ingram , E.H. Stitt
      The performance of Kenics KM static mixers has been determined for the blending of two shear-thinning fluid streams with identical or different rheology. Planar Laser Induced Fluorescence (PLIF) has been used to obtain the concentration distribution at the mixer outlet by doping one fluid stream with fluorescent dye upstream of the mixer inlet. The effect of scale of the static mixer, total flow rate, flow ratio between the fluid streams and inlet configuration have been investigated. The applicability of different methods to characterise mixing performance is examined by comparing conventional mixing measures such as coefficient of variation and maximum striation area against recent alternative methods presented in the literature, such as the areal distribution method developed by Alberini et al. (2014). A method of characterising individual striations by determining their distribution as a function of size and concentration is also presented. These findings illustrate the complexity of information-rich PLIF images, and highlight how different methods of analysis may be appropriate given the dependencies of the downstream process.


      PubDate: 2015-02-05T13:54:02Z
       
  • Effect of ultrasound on mass transfer during electrodeposition for
           electrodes separated by a narrow gap
    • Abstract: Publication date: 3 July 2014
      Source:Chemical Engineering Science, Volume 113
      Author(s): S. Coleman , S. Roy
      This work reports an investigation on mass transfer by ultrasound agitation during electrodeposition on electrodes separated by a narrow inter-electrode gap. Polarisation experiments were performed to identify the mass transfer limiting current. The limiting current density was used to calculate mass transfer boundary layer thicknesses which were used to develop mass transfer correlations. Experiments were carried out using a cell with parallel copper discs which were positioned at gaps of 1, 0.5 and 0.15cm. The distance between the ultrasonic probe and electrodes was varied between 3 and 1.5cm. The polarisation data showed clear limiting current plateaux when the distance between the electrodes was larger, however significant distortions were observed when the gap was 0.15cm. It was found that lower ultrasound powers of 9–18W/cm2 provided more effective agitation at narrower electrode gaps than powers exceeding 18W/cm2. Sherwood correlations showed that in this system, developing turbulence occurs for larger inter-electrode spacing, whereas for narrow electrode gaps fully turbulent correlations were obtained. A 2-D current distribution model showed that potential distortions that were observed in the polarisation data were caused by the close placement of the metallic US probe to the two parallel electrodes.


      PubDate: 2015-02-05T13:54:02Z
       
  • Operating ranges of gas–liquid capillary microseparators:
           Experiments and theory
    • Abstract: Publication date: 26 July 2014
      Source:Chemical Engineering Science, Volume 114
      Author(s): Mark D. Roydhouse , Marc Pradas , Noor Al-Rifai , Benjamin Azizi , Enhong Cao , Serafim Kalliadasis , Asterios Gavriilidis
      An experimental and theoretical study of capillary gas/liquid phase microseparators is presented. The device studied comprises a main microchannel with a set of capillaries fabricated to each side so that the liquid (wetting) phase can be separated from the gas (non-wetting) phase due to capillary effects. Different units are employed with different characteristics of capillaries (constant or tapered cross-sectional area and capillary size). We study how complete separation depends on the externally controlled pressure difference at the liquid and the gas outlet and how separation is affected by the imposed inlet flow rate. The results demonstrate that the operability pressure window becomes narrower as the fluid flow rates increase, and reveal discrepancies with theoretical predictions based on a simple Hagen–Poiseuille formulation. This is addressed by a new equation that takes into account interface curvature effects, and is found to be in qualitative agreement with the experimental results. In addition, we perform CFD simulations observing the emergence of interface breaking at high flow rates.


      PubDate: 2015-02-05T13:54:02Z
       
  • On the optimal design of gas-expanded liquids based on process performance
    • Abstract: Publication date: 1 August 2014
      Source:Chemical Engineering Science, Volume 115
      Author(s): Eirini Siougkrou , Amparo Galindo , Claire S. Adjiman
      Gas-expanded liquids (GXLs) are mixed solvents composed of an organic solvent and a compressible gas, usually carbon dioxide (CO2) due to its environmental and economic advantages. The best choice of GXL, as defined by the specific organic solvent and the CO2 composition, depends strongly on the process in which the solvent is to be used. Given the large range of possible choices, there is a need to predict the impact of GXL design on process performance from economic and environmental perspectives. In this work, we present a design methodology in which limited experimental data are used to build a predictive model which allows a wider design space to be assessed. The proposed methodology for the integrated design of CO2-expanded solvent and process is applied to the Diels–Alder reaction of anthracene and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD). Three organic co-solvents are studied: acetonitrile, methanol and acetone. Given that the process cost is sensitive to the operating pressure and reactor volume, a trade-off between reaction rate constant and solubility is required in order to design an optimal process from a cost perspective. From a total cost perspective and in terms of energy consumption, it is found that designs with small amounts of CO2 or, in the case of acetone, without any CO2, offer the best performance. However, CO2 use is found to lead to a significant reduction in organic solvent inventory, up to 70 % in some cases. In this work the importance of taking multiple performance criteria, including process metrics, into account when designing GXLs is demonstrated.


      PubDate: 2015-02-05T13:54:02Z
       
  • Continuous protein refolding in a tubular reactor
    • Abstract: Publication date: 6 September 2014
      Source:Chemical Engineering Science, Volume 116
      Author(s): Siqi Pan , Monika Zelger , Rainer Hahn , Alois Jungbauer
      Continuous protein refolding by direct dilution was established in a laboratory-scale tubular reactor. Advanced refolding strategies by pulsed refolding and temperature leap, favoring the native pathway of specific model proteins were also implemented. The reactor was tested with two autoprotease fusion proteins, EDDIE-pep6His and 6His-EDDIE-GFPmut3.1, and also on carbonic anhydrase II. Direct refolding kinetics approximated by a folding kinetic of first order and aggregation kinetic of second order was similar to batch processes, while pulse and temperature leap refolding yields were higher than direct batch refolding method. Productivity comparisons calculated as amount of refolded protein per reactor volume and process time showed that an optimal refolding concentration to achieve highest productivity value is a balance between a rational reactor volume and a reasonable refolding time. Productivity in a tubular reactor is always higher as emptying and refilling times required for batch reactor decreases productivity. This productivity improvement is higher for a fast refolding protein than a slower one.


      PubDate: 2015-02-05T13:54:02Z
       
  • Capturing CO2 from ambient air using a polyethyleneimine–silica
           adsorbent in fluidized beds
    • Abstract: Publication date: 6 September 2014
      Source:Chemical Engineering Science, Volume 116
      Author(s): Wenbin Zhang , Hao Liu , Chenggong Sun , Trevor C. Drage , Colin E. Snape
      Carbon Capture and Storage (CCS) uses a combination of technologies to capture, transport and store carbon dioxide (CO2) emissions from large point sources such as coal or natural gas-fired power plants. Capturing CO2 from ambient air has been considered as a carbon-negative technology to mitigate anthropogenic CO2 emissions in the air. The performance of a mesoporous silica-supported polyethyleneimine (PEI)–silica adsorbent for CO2 capture from ambient air has been evaluated in a laboratory-scale Bubbling Fluidized Bed (BFB) reactor. The air capture tests lasted for between 4 and 14 days using 1kg of the PEI–silica adsorbent in the BFB reactor. Despite the low CO2 concentration in ambient air, nearly 100% CO2 capture efficiency has been achieved with a relatively short gas–solid contact time of 7.5s. The equilibrium CO2 adsorption capacity for air capture was found to be as high as 7.3wt%, which is amongst the highest values reported to date. A conceptual design is completed to evaluate the technological and economic feasibility of using PEI–silica adsorbent to capture CO2 from ambient air at a large scale of capturing 1Mt-CO2 per year. The proposed novel “PEI-CFB air capture system” mainly comprises a Circulating Fluidized Bed (CFB) adsorber and a BFB desorber with a CO2 capture capacity of 40t-CO2/day. Large pressure drop is required to drive the air through the CFB adsorber and also to suspend and circulate the solid adsorbents within the loop, resulting in higher electricity demand than other reported air capture systems. However, the Temperature Swing Adsorption (TSA) technology adopted for the regeneration strategy in the separate BFB desorber has resulted in much smaller thermal energy requirement. The total energy required is 6.6GJ/t-CO2 which is comparable to other reference air capture systems. By projecting a future scenario where decarbonization of large point energy sources has been largely implemented by integration of CCS technologies, the operating cost under this scenario is estimated to be $108/t-CO2 captured and $152/t-CO2 avoided with an avoided fraction of 0.71. Further research on the proposed 40t-CO2/day ‘PEI-CFB Air Capture System’ is still needed which should include the evaluation of the capital costs and the experimental investigation of air capture using a laboratory-scale CFB system with the PEI–silica adsorbent.


      PubDate: 2015-02-05T13:54:02Z
       
  • A model based approach for identifying robust operating conditions for
           industrial chromatography with process variability
    • Abstract: Publication date: 6 September 2014
      Source:Chemical Engineering Science, Volume 116
      Author(s): Edward J. Close , Jeffrey R. Salm , Daniel G. Bracewell , Eva Sorensen
      A model based approach has been developed and used to identify robust operating conditions for an industrial hydrophobic interaction chromatography where resin lot variability, combined with feed stream variability, was resulting in serious performance issues during the purification of a multi component therapeutic protein from crude feed material. An equilibrium dispersive model was formulated which successfully predicted the key product critical quality attribute during validation studies. The model was then used to identify operating parameter ranges that assured product quality despite the process variability. Probabilistic design spaces were generated using stochastic simulations that showed the probability that each resin lot would meet product quality specifications, over a range of possible operating conditions, accounting for the historical variability experienced in the load material composition and concentration. No operating condition was found with normal process variability where quality assurance remained >0.95 for resins that gave the highest and lowest product recoveries during process development. The lowest risk of batch failure found was 16%, and operating conditions were not robust. We then extended the stochastic methodology used to generate probabilistic design spaces, to identify the level of control required on the load material composition and concentration to bring process robustness to an acceptable level, which is not possible using DOE experimental methods due to the impractical amount of resources that would be required. Although reducing inlet variability resulted in an increase in the assurance of product quality, the results indicated that changing operating conditions according to which resin lot is in use is the favorable option.


      PubDate: 2015-02-05T13:54:02Z
       
  • Scalability of mass transfer in liquid–liquid flow
    • Abstract: Publication date: 6 September 2014
      Source:Chemical Engineering Science, Volume 116
      Author(s): A. Woitalka , S. Kuhn , K.F. Jensen
      We address liquid–liquid mass transfer between immiscible liquids using the system 1-butanol and water, with succinic acid as the mass transfer component. Using this system we evaluate the influence of two-phase flow transitions from Taylor flow to stratified flow and further to dispersed flow at elevated flow rates. In addition, we address the scale-up behavior of mass transfer coefficients and the extraction efficiency by using reactors on the micro- and the milli-scale. Flow imaging enables us to identify the different flow regimes and to connect them to the trends observed in mass transfer, and the obtained results highlight the dependence of mass transfer on flow patterns. Furthermore, the results show that on the milli-scale fluid–structure interactions are driving the phase dispersion and interfacial mass transfer, and such a reactor design ensures straightforward scalability from the micro- to the milli-scale.


      PubDate: 2015-02-05T13:54:02Z
       
  • Attrition of paracetamol and aspirin under bulk shear deformation
    • Abstract: Publication date: Available online 22 October 2014
      Source:Chemical Engineering Science
      Author(s): C. Hare , M. Ghadiri
      Particles are frequently exposed to shear stresses during manufacturing, which leads to breakage. This is particularly relevant to weak active pharmaceutical ingredients and is prevalent in pharmaceutical and food industries. The attrition of paracetamol and aspirin caused by shear deformation at very low stresses is investigated here. The extent of breakage of these particles is related to the prevailing shear stresses and strains. In contrast to the expected trend, smaller particles exhibited increased breakage rates. At the onset of shearing at low stresses aspirin particles experienced slightly more breakage than the paracetamol, however prolonged shearing resulted in greater breakage of paracetamol. Breakage occurred initially through chipping with some fragmentation, particularly more noticeable for aspirin, with an increase in abrasion after extensive shear strain for paracetamol. Empirical breakage relationships are proposed and when combined with process stresses and strain analyses the extent of breakage occurring in process equipment can be estimated.
      Graphical abstract image

      PubDate: 2015-02-05T13:54:02Z
       
 
 
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